The illegal copying of digital multimedia data products (such as movies and audio recordings) is a widespread problem. The problem only seems to be growing, despite technical advancements in copy protection and mounting efforts to enforce intellectual property rights. This infringement of intellectual property rights can cause great financial harm to the owner.
The upward trend in illegal copying seems to be tied to the expanding use of digital media and equipment for storing and distributing digital multimedia data. The enormous growth of Internet technology and digitally stored data has made it possible to easily and inexpensively produce high-quality identical copies of an original. In addition, it is possible to make the copies available to the entire Internet community. This process has become further easier with the usage of peer-to-peer (P2P) networks. With the increasing availability of copying devices and increased bandwidth for digital data, the need to restrain illegal redistribution of digital multimedia data (such as images,. videos and music) has become an important issue.
One way to deter illegal copying is to increase the risk of being caught after the piracy has occurred. Storing a unique, invisible mark in each copy (in other words, embedding the mark in the perceptual content of the digital media signal securely and robustly) is a way to increase that risk. In this manner, if an illegal copy is found somewhere, it is possible to find the owner of the copy and to take legal action. This type of enforcement scheme is called fingerprinting (also known as “mark embedding” for forensics in some communities).
The idea of fingerprinting is to uniquely mark each copy. This makes each copy bit-wise different from every other copy, and yet otherwise perceptually approximately the same. In this way, it is possible to distinguish between all legal copies. The marking can be used to identify the copy, and thereby the user if his identity is linked to the fingerprint in some way. For example, if the fingerprinted copies are only distributed to those persons who identify themselves, it may be possible, if an illegal copy is found, to identify the owner of the legal copy from which the illegal copy was made.
By way of example, assume the owner of a movie on digital video disk (DVD) makes copies of the movie for sale. Each of the copies is fingerprinted. The owner only sells a copy to a user after having individually and uniquely marked each user's copy with a fingerprint and associated each fingerprint uniquely with a buyer. Later, a number of buyers, called pirates, collude in creating an illegal copy that they redistribute (in this situation the pirates are also called colluders). The owner of the movie can analyze an illegal copy and attempt to find out which of the buyers took part in the creation of the illegal copy.
The fingerprinting technique includes inserting fingerprints in each copy of a digital product using a watermarking (also termed “mark embedding”) scheme. A watermarking scheme imperceptibly embeds the fingerprint in the perceptual content in a way that it can only be recovered using a secure key. It should be noted that this type of scheme is completely different from conventional Digital Rights Management (DRM) techniques for content protection. There are two important differences between watermarks (for screening purposes to prevent illegal copying or recording) and fingerprints (for forensics purposes to trace the leakage). First, while in watermarking the hidden message (mark) is the same for all buyers (and this mark often represents the identity of the content owner), in fingerprinting the mark depends on the buyer's identity. Second, buyer collusion is not an issue in watermarking (the marked copies for a single content being the same for all buyers). However, in fingerprinting the mark is different for every buyer, and it makes sense for a collusion of buyers to collude by comparing their copies and try to locate and delete some mark bits. Thus, in a collusion attack on fingerprinted digital products, a group of dishonest users colludes to create an illegal copy that hides their identities by putting together different parts of their copies. The attack seeks to eliminate the hidden embedded fingerprints.
One problem with current fingerprinting techniques is that they are limited in the number of collaborators that can be identified. For example, several traditional current fingerprinting techniques can only identify between four and eight collaborators. Some newer fingerprinting techniques use fingerprinting codes to enable the detection of an order of magnitude better that traditional fingerprinting techniques. However, there are frequently a large number of collaborators involved in the production of an illegal copy. This means that current fingerprinting techniques cannot accurately detect and identify collaborators greater than one-hundred. This severely limits the deterrent effect of fingerprinting, since collaborators know that all they have to do is collaborate with a large number of other copy owners to avoid detection.
Another problem with current fingerprinting techniques is that they are susceptible to estimation attacks. Estimation attacks occur when attackers take all of the frames of the scene and compute an average of all the frames, thereby forming an estimate of the original unmarked content. Alternatively, different techniques may also be used to estimate the fingerprint of each client using the inherent redundancy that is present in the media signal. This tends to greatly weaken or eliminate all of the fingerprints. Therefore, what is needed is a fingerprinting system and method that is capable of accurately identifying at least an order of magnitude greater number of collaborators than current fingerprinting techniques. What is also needed is a fingerprinting system and method that is (cryptographically) secure and resistant to estimation attacks.